‘In this post we argue that as a matter of domestic constitutional law, the Prime Minister is unable to issue a declaration under Article 50 of the Lisbon Treaty – triggering our withdrawal from the European Union – without having been first authorised to do so by an Act of the United Kingdom Parliament. Were he to attempt to do so before such a statute was passed, the declaration would be legally ineffective as a matter of domestic law and it would also fail to comply with the requirements of Article 50 itself.’